1. Field of the Invention
The present invention relates to remote staged radiant wall furnace burner configurations, and more particularly, to the placement of secondary gas nozzles remote from the radiant wall burner nozzles resulting in lower NOX production.
2. Description of the Prior Art
Radiant wall gas burner furnaces are well known and have been used in reforming and cracking operations and the like for many years. Radiant wall burners generally include central fuel gas-air mixture burner tubes surrounded by annular refractory tiles which are adapted for insertion into openings in the furnace wall. The burner nozzles discharge fuel gas-air mixtures in directions generally parallel and adjacent to the internal faces of the refractory tiles. The combustion of the fuel gas-air mixtures causes the faces of the burner tiles to radiate heat, e.g., to process tubes, and undesirable flame impingement on the process tubes is thereby avoided.
Radiant wall burners are typically installed in several rows along a furnace wall. This type of configuration is usually designed to provide uniform heat input to the process from the wall area comprising the radiant wall burner matrix.
More stringent environmental emission standards are continuously being imposed by governmental authorities which limit the quantities of gaseous pollutants such as oxides of nitrogen (NOX). Such standards have led to the development of staged or secondary fuel burner apparatus and methods wherein all of the air and some of the fuel is burned in a first zone and the remaining fuel is burned in a second downstream zone. In such staged fuel burner apparatus and methods, an excess of air in the first zone functions as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NOX. Desirably, furnace flue gas functions as a diluent to lower the temperature of the burning secondary fuel and thereby reduces the formation of NOX.
Similarly, staged radiant wall burner designs have also been developed wherein the burners radially combust a primary fuel lean mixture of fuel gas and air and stage fuel risers supply the stage tips with secondary fuel. The location of the secondary fuel tips can vary, depending on the manufacturer and type of burner, but they are typically located either in the center of the burner tip or around and adjacent to the perimeter of the tip.
While the staged radiant wall burners and furnace designs have been improved whereby combustion gases containing lower levels of pollutants are produced, additional improvement is necessary. Thus, there is a need for improved methods of burning fuel gas and air using radiant wall burners whereby combustion gases having lower pollutant levels are produced.